Neutrophil and macrophage cells express several proteins which defend the host from invading bacteria. The main goals of this project are to study the antimicrobial activity of a small group of proteins called defensins and to identify new macrophage specific gene products that might regulate bacterial killing. During the current year, employing cDNA sequencing approach, I have identified a large number of new genes that are expressed in a human macrophage cell line. For this purpose, a high quality cDNA library was constructed using THP-1 cell mRNA. Thus far 75 genes have been isolated. These genes were identified by extensive sequence analysis. All the characterized cDNAs contained an identifiable open reading frame. Among the newly discovered genes are a new superoxide dismutase (SOD) gene. The protein sequence encoded by this new SOD gene shows all the functional motifs of a CuZn SOD enzyme. However, at the DNA level the gene is distinct from the known cytoplasmic SOD. Another newly discovered gene product shows considerable homology to nematode chitinases. Other newly discovered genes include a macrophage specific proteinase inhibitor, tyrosine kinase gene, and a gene coding for a nuclear regulatory protein. A small percentage of the characterized cDNAs shows no homology to any of the known proteins. The primary structure of about l2 genes have been completely determined. This work required extensive DNA sequence analysis. For this purpose, I have constructed a new plasmid vector with features for rapid and simplified subcloning.